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/** @file Implementation of the Terragen importer class */

#include "AssimpPCH.h"

#ifndef ASSIMP_BUILD_NO_TERRAGEN_IMPORTER
#include "TerragenLoader.h"

using namespace Assimp;

static const aiImporterDesc desc = {
	"Terragen Heightmap Importer",
	"",
	"",
	"http://www.planetside.co.uk/",
	aiImporterFlags_SupportBinaryFlavour,
	0,
	0,
	0,
	0,
	"ter" 
};

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
TerragenImporter::TerragenImporter()
: configComputeUVs (false)
{}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well 
TerragenImporter::~TerragenImporter()
{}

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file. 
bool TerragenImporter::CanRead( const std::string& pFile, IOSystem* pIOHandler, bool checkSig) const
{
	// check file extension 
	std::string extension = GetExtension(pFile);
	
	if( extension == "ter")
		return true;

	if(  !extension.length() || checkSig)	{
		/*  If CanRead() is called in order to check whether we
		 *  support a specific file extension in general pIOHandler
		 *  might be NULL and it's our duty to return true here.
		 */
		if (!pIOHandler)return true;
		const char* tokens[] = {"terragen"};
		return SearchFileHeaderForToken(pIOHandler,pFile,tokens,1);
	}
	return false;
}

// ------------------------------------------------------------------------------------------------
// Build a string of all file extensions supported
const aiImporterDesc* TerragenImporter::GetInfo () const
{
	return &desc;
}

// ------------------------------------------------------------------------------------------------
// Setup import properties
void TerragenImporter::SetupProperties(const Importer* pImp)
{
	// AI_CONFIG_IMPORT_TER_MAKE_UVS
	configComputeUVs = ( 0 != pImp->GetPropertyInteger(AI_CONFIG_IMPORT_TER_MAKE_UVS,0) );
}

// ------------------------------------------------------------------------------------------------
// Imports the given file into the given scene structure. 
void TerragenImporter::InternReadFile( const std::string& pFile, 
	aiScene* pScene, IOSystem* pIOHandler)
{
	IOStream* file = pIOHandler->Open( pFile, "rb");

	// Check whether we can read from the file
	if( file == NULL)
		throw DeadlyImportError( "Failed to open TERRAGEN TERRAIN file " + pFile + ".");

	// Construct a stream reader to read all data in the correct endianess
	StreamReaderLE reader(file);
	if(reader.GetRemainingSize() < 16)
		throw DeadlyImportError( "TER: file is too small" );

	// Check for the existence of the two magic strings 'TERRAGEN' and 'TERRAIN '
	if (::strncmp((const char*)reader.GetPtr(),AI_TERR_BASE_STRING,8))
		throw DeadlyImportError( "TER: Magic string \'TERRAGEN\' not found" );

	if (::strncmp((const char*)reader.GetPtr()+8,AI_TERR_TERRAIN_STRING,8))
		throw DeadlyImportError( "TER: Magic string \'TERRAIN\' not found" );

	unsigned int x = 0,y = 0,mode = 0;
	float rad  = 6370.f;
	(void)rad;


	aiNode* root = pScene->mRootNode = new aiNode();
	root->mName.Set("<TERRAGEN.TERRAIN>");

	// Default scaling is 30
	root->mTransformation.a1 = root->mTransformation.b2 = root->mTransformation.c3 = 30.f;

	// Now read all chunks until we're finished or an EOF marker is encountered
	reader.IncPtr(16);
	while (reader.GetRemainingSize() >= 4)	
	{
		const char* head = (const char*)reader.GetPtr();
		reader.IncPtr(4);

		// EOF, break in every case
		if (!::strncmp(head,AI_TERR_EOF_STRING,4))
			break;

		// Number of x-data points
		if (!::strncmp(head,AI_TERR_CHUNK_XPTS,4))
		{
			x = (uint16_t)reader.GetI2();
		}
		// Number of y-data points
		else if (!::strncmp(head,AI_TERR_CHUNK_YPTS,4))
		{
			y = (uint16_t)reader.GetI2();
		}
		// Squared terrains width-1. 
		else if (!::strncmp(head,AI_TERR_CHUNK_SIZE,4))
		{
			x = y = (uint16_t)reader.GetI2()+1;
		}
		// terrain scaling
		else if (!::strncmp(head,AI_TERR_CHUNK_SCAL,4))
		{
			root->mTransformation.a1 = reader.GetF4();
			root->mTransformation.b2 = reader.GetF4();
			root->mTransformation.c3 = reader.GetF4();
		}
		// mapping == 1: earth radius
		else if (!::strncmp(head,AI_TERR_CHUNK_CRAD,4))
		{
			rad = reader.GetF4();
		}
		// mapping mode
		else if (!::strncmp(head,AI_TERR_CHUNK_CRVM,4))
		{
			mode = reader.GetI1();
			if (0 != mode)
				DefaultLogger::get()->error("TER: Unsupported mapping mode, a flat terrain is returned");
		}
		// actual terrain data
		else if (!::strncmp(head,AI_TERR_CHUNK_ALTW,4))
		{
			float hscale  = (float)reader.GetI2()  / 65536;
			float bheight = (float)reader.GetI2();

			if (!hscale)hscale = 1;

			// Ensure we have enough data
			if (reader.GetRemainingSize() < x*y*2)
				throw DeadlyImportError("TER: ALTW chunk is too small");

			if (x <= 1 || y <= 1)
				throw DeadlyImportError("TER: Invalid terrain size");

			// Allocate the output mesh
			pScene->mMeshes = new aiMesh*[pScene->mNumMeshes = 1];
			aiMesh* m = pScene->mMeshes[0] = new aiMesh();

			// We return quads
			aiFace* f = m->mFaces = new aiFace[m->mNumFaces = (x-1)*(y-1)];
			aiVector3D* pv = m->mVertices = new aiVector3D[m->mNumVertices = m->mNumFaces*4];
			
			aiVector3D *uv( NULL );
			float step_y( 0.0f ), step_x( 0.0f );
			if (configComputeUVs) {
				uv = m->mTextureCoords[0] = new aiVector3D[m->mNumVertices];
				step_y = 1.f/y;
				step_x = 1.f/x;
			}
			const int16_t* data = (const int16_t*)reader.GetPtr();

			for (unsigned int yy = 0, t = 0; yy < y-1;++yy)	{
				for (unsigned int xx = 0; xx < x-1;++xx,++f)	{

					// make verts
					const float fy = (float)yy, fx = (float)xx;
					register unsigned tmp,tmp2;
					*pv++ = aiVector3D(fx,fy,    (float)data[(tmp2=x*yy)    + xx] * hscale + bheight);
					*pv++ = aiVector3D(fx,fy+1,  (float)data[(tmp=x*(yy+1)) + xx] * hscale + bheight);
					*pv++ = aiVector3D(fx+1,fy+1,(float)data[tmp  + xx+1]         * hscale + bheight);
					*pv++ = aiVector3D(fx+1,fy,  (float)data[tmp2 + xx+1]         * hscale + bheight);

					// also make texture coordinates, if necessary
					if (configComputeUVs) {
						*uv++ = aiVector3D( step_x*xx,     step_y*yy,     0.f );
						*uv++ = aiVector3D( step_x*xx,     step_y*(yy+1), 0.f );
						*uv++ = aiVector3D( step_x*(xx+1), step_y*(yy+1), 0.f );
						*uv++ = aiVector3D( step_x*(xx+1), step_y*yy,     0.f );
					}

					// make indices
					f->mIndices = new unsigned int[f->mNumIndices = 4];
					for (unsigned int i = 0; i < 4;++i)
						f->mIndices[i] = t++;
				}
			}

			// Add the mesh to the root node
			root->mMeshes = new unsigned int[root->mNumMeshes = 1];
			root->mMeshes[0] = 0;
		}

		// Get to the next chunk (4 byte aligned)
		unsigned dtt;
		if ((dtt = reader.GetCurrentPos() & 0x3))
			reader.IncPtr(4-dtt);
	}

	// Check whether we have a mesh now
	if (pScene->mNumMeshes != 1)
		throw DeadlyImportError("TER: Unable to load terrain");

	// Set the AI_SCENE_FLAGS_TERRAIN bit
	pScene->mFlags |= AI_SCENE_FLAGS_TERRAIN;
}

#endif // !! ASSIMP_BUILD_NO_TERRAGEN_IMPORTER
